The present invention is directed to an improved method and apparatus for casting, hot rolling and annealing non-heat treatable aluminum alloys and, in particular, to a method of heating a cast and hot rolled aluminum alloy sheet using infrared heating directly after hot rolling to continuously produce an annealed aluminum alloy product, thereby eliminating the need for multiple processing lines. This elimination of multiple processing lines results in superior economies of production through both reduced capital expense and the elimination of inventory of coiled products in intermediary stages of processing. This invention is especially suitable for the manufacture of transportation products, such as automotive structural sheet.
One of the problems when processing metals, including aluminum, is the accumulation of inventory during processing and the costs associated with maintaining and storing such inventory. These problems are most significant during the production of aluminum sheet through conventional ingot metallurgy. In conventional ingot processing, multiple processing lines are required to take the cast ingot to its final form of annealed coiled product, with inventory capacity required for nearly every intermediary product form. For ingot processing, these processing steps include: casting; homogenizing; hot rolling; intermediate annealing; cold rolling (roughing mill); cold rolling (finish mill); and coil annealing. When the ingot is cast, the ingots are inventoried prior to re-heating to the homogenization treatment. When the ingot is hot rolled, the hot rolled coils are stored prior to further processing. Similarly, cold rolled coils also require storage prior to the cold roll finishing pass and annealing processing steps.
Much of the inventory problem created by ingot casting has been solved through the use of continuous casting followed by in-line hot rolling. This processing method eliminates the re-heating of ingots and the inventory problem associated with storing the ingots prior to homogenization. However, inventory problems still exist in connection with the secondary processing of aluminum. That is, once the cast product is hot rolled, the hot rolled coils must still be stored prior to further processing. As such, a need has developed to provide improved apparatus and processing techniques to overcome the drawbacks associated with present day processing.
The invention solves this problem by combining continuous casting, direct hot rolling and infrared heating of non-heat treatable aluminum alloy products into a single production line. With the invention, a final annealed product is produced in coiled form without the production of intermediate product forms. Additionally, this process significantly reduces energy consumption used in the annealing step by exploiting the residual latent heat of the hot rolled product in the annealing process.
The use of in-line heating of metal alloys is well known. U.S. Pat. No. 5,739,506 to Hanton et al. discloses an example of an induction heating system which relates to transverse flux heating. These heating systems are desirable when treating a variety of widths of strip or sheet metal. Similarly, U.S. Pat. No. 5,990,464 to Hino et al. discloses an example of in-line inductive heating of hot rolled steel sheet, wherein inductive heating is imposed between stands of a multi-stand rolling mill.
Induction heating and processing of aluminum is also disclosed in U.S. Pat. No. 5,562,784 to Nishikawa et al. This patent is directed to an aluminum alloy substrate for electrolytically grainable lithographic printing plate. In making this material, the aluminum alloy is continuously cast. The cast material can then be either cold rolled or hot rolled and subsequently cold rolled. The strip is heat treated for recrystallization in the course of cold rolling. The heat treatment is disclosed as either a continuous annealing furnace or a transverse flux induction heater. The induction heating of Nishikawa et al. is associated with recrystallization after cold rolling and is not part of an apparatus or method which continuously casts, hot rolls and heats the hot rolled strip using an infrared heating method to produce a non-heat treatable aluminum alloy into a final annealed product.
Accordingly, it is a first object of the present invention to provide an apparatus and method which produce non-heat treatable aluminum alloys in an economical fashion.
Another object of the present invention is a method of eliminating the need for excessive inventory during processing of cast and hot rolled non-heat treatable aluminum alloys.
Another object of the present invention is a method of reducing the energy required for annealing of non-heat treatable aluminum alloys by using the residual heat latent in the hot rolled sheet product.
One other object of the present invention is an apparatus for processing non-heat treatable aluminum alloys using infrared heating and a feedback control system for annealing and control thereof.
A further object of the present invention is a method and apparatus that use accumulators at the entrance and exit sides of an infrared heating apparatus positioned inline with continuous casting and hot rolling equipment to allow for the production of annealed coils of non-heat treatable aluminum sheet products in a continuous fashion.
One other object of the present invention is a method and apparatus that use quenching devices at the exit side of an infrared heating apparatus positioned in-line with continuous casting and hot rolling equipment to allow for the production of annealed coils of non-heat treatable aluminum sheet products in a continuous fashion.
Other objects and advantages of the present invention will become apparent as a description thereof proceeds.
In satisfaction of the foregoing objects and advantages, the present invention comprises an improvement in a method of casting, hot rolling and annealing non-heat treatable aluminum alloys, whereby a cast product is directly hot rolled to form a hot rolled product, and the hot product is annealed to form an annealed product. According to the invention, the hot rolled product is directly heated using an infrared heat source, the heating is performed from an elevated temperature caused by the latent heat in the hot rolled product to a final annealing temperature to form a final annealed product. The infrared heating is controlled using a feedback control based on at either a direct temperature measurement of the hot rolled sheet or an inferred temperature based on other operating parameters. The surface of the final annealed product can be protected prior to coiling. The protection can include oiling or using an interleaving material. Preferably, the elevated temperature exiting the hot rolling step is between 400xc2x0 and 600xc2x0 F. (204 to 316xc2x0 C.) and the final annealing temperature ranges between 650xc2x0 and 1000xc2x0 F. (343 to 538xc2x0 C.). In addition, belt casting is a preferred mode for the inventive method. The feedback control can use a direct measure of the elevated temperature of the hot rolled product and/or a measure of the temperature of the final annealed product after heating is completed, or an inferred temperature calculated from the known physical properties of the alloy being heated and operating parameters, i.e., the line speed, the mill power, the lubricant flow rate, the mill reduction schedule, etc.
The present invention also includes an apparatus for practicing the inventive method (the apparatus including a caster) a hot rolling mill and an annealing furnace. The annealing furnace is an infrared heating device positioned directly downstream of the hot rolling mill for annealing the hot rolled product to a final annealing temperature as described above. The apparatus may also include a cooling device which can be a quench device, either air, water or a combination of both. An oiler can be interposed downstream of the infrared heating device and the final anneal product recovery.
Accumulation can also be utilized in conjunction with the invention, both prior to and downstream of the infrared heating device. The accumulation can be accomplished by using conventional strip accumulators, or coilers, flying shears or the like as a means to recover the hot rolled product or product downstream of the infrared heating device, if so desired.
One other object of the present invention is a method and apparatus that uses a shear before or after the infrared heating apparatus followed by the dual recoilers positioned in-line with continuous casting and hot rolling equipment to allow for the production of annealed coils of non-heat treatable aluminum sheet products in a continuous fashion.